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Comparative studies on conventional and microwave-assisted synthesis of novel indole derivatives and their antimicrobial activities

Doddappa Pralhad Anekal, J.S.Biradar

The 2, 5-disubstituted Indole 3-carboxaldehydes (1a-e) on crossed aldol condensation reaction with 2-acetoacetamido-pyridine (2) yields (E)-2- ((5’,2’-disubstituted-1H-indol-3-yl)methylene)-3-oxo-N-(pyridine-2”-yl) butanamides (3a-e). The (E)-2-((5’, 2’-disubstituted-1H-indol-3-yl)methylene)- 3-oxo-N-(pyridine-2”-yl) butanamides (3a-e) undergoes cyclocondensation reaction with hydrazine hydrate in the presence of glacial acetic acid in ethanol yields 1-acetyl-5-(5’,2’-disbstituted-1H-indol-3-yl)-4,5-dihydro- 3-methyl-N-(pyridine-2-yl)-1H-pyrazole-4-carboxamides (4a-e) andwith hydroxyl amine hydrochloride in the presence of potassiumhydroxide yields 5-(5’,2’-disubstituted-1H-indol-3-yl)-4,5-dihydro-3-methyl-N-(pyrido-2-yl) isoxazole-4-carboxamides (5a-e). These Indole derivatives were synthesized under conventional and microwave assisted conditions and found evidently that Microwave irradiation method reduces time of reactions, improves the yields and reproducibility over conventional method. The structures of the products thus obtained are confirmed by their analytical and spectroscopic analysis. Newly synthesized compounds (3a-e), (4a-e) and (5a-e) were evaluated for In-vitro antimicrobial activities against various microbial strains and most of the molecules have displayed significant antimicrobial activities.